It has been suggested, for example in U.S. Pat. No. 17,114 to Pearce et al, dated Apr. 21, 1857; U.K. Patent 106,394 to Pattison, dated May 24, 1917; and U.S. Pat. No. 2,179,100 to Ramsay, dated Nov. 7, 1939, that railcars be unloaded by rolling them in a cradle which rolls on a cradle track. The track extends laterally relative to the longitudinal axes of the car and cradle, thus causing lateral translation of the car axis as the car rotates about that axis. The apparatus required to power and control the rotary-lateral motion in such dumpers has proved unsatisfactory in the past for a number of reasons, not the least of which have been cumbersomeness and slowness in operation. This no doubt is one of the reasons why these dumpers have not fared better in competition with the common rotary tipple type dumpers exemplified by U.S. Pat. Nos. 2,552,186 to Koehler, et al, dated May 8, 1951; 2,575,869 to Flowers, dated Nov. 20, 1951; and 3,811,580 to Sheppard, dated May 21, 1974.
More recent types of rotary-lateral dumpers which we refer to as gravity-only dumpers seek to preempt the above-described problems of rotary-lateral dumpers by shaping the profile of the arcuate cradle track-engaging rocker members in a special way. For example, see U.S. Pat. No. 4,432,688 to Schmidt, dated Feb. 21, 1984, in which the rocker profile conforms to an equation such that the profile will cause the cradle and car, when released, to pass along the cradle track from car-receiving position to car-dumping position and back again solely through the action of gravity, the return motion being assisted by the change in center of gravity of the car which occurs on discharge of its contents and by counterweights lifted during the dumping action. In other words, no external power source is used. Gravity only dumpers operate very rapidly and are quite simple, but are subject to a variety of disadvantages relating in general to proper control and completion of the dumping operation.
We believe however that there is a need for further improvements in rotary-lateral dumpers which provide for controlled motion of the cradle and car with good operating speed, while avoiding the complexity and cumbersomeness which have heretofore impeded wide acceptance of dumpers of this general category. The purpose of the present invention is to fulfill this need.